The locus for multiple endocrine neoplasia, type 2A (MEN-2A), a dominantly inherited cancer syndrome, has been mapped to the pericentromeric region of chromosome 10. The MEN-2A syndrome involves medullary thyroid carcinoma (MTC), pheochromocytoma (PHEO), and hyperparathyroidism. Two other related inherited cancer syndromes, MEN-2B and MTC without PHEOS, also map to the same region of chromosome 10. The highly informative markers that are close to and flank the MEN2A locus allow most family members in MEN-2A kindreds to be identified as carriers or non-carriers with high probabilities. This is a significant advance since the ability to identify presymptomatic carriers allows much more effective biochemical screening for early signs of malignancy and prevention of metastasis. During the previous grant period, we found the first evidence for MEN-2A being on chromosome 10 and contributed significantly to its fine-scale genetic mapping near the centromere of 10. We have begun work to identify the smallest molecular region that co-segregates with the abnormal allele and then clone most of that region as the next step toward the positional cloning of the MEN2A gene itself. We propose continuing those efforts using the resources we have assembled. We will use a cloning strategy based on yeast artificial chromosomes using many nucleation sites from which to clone and then walk. There are many built-in safeguards to overcome the inherent ambiguities in any one method for mapping and ordering these clones. Our hypothesis is that the MEN2A region is about 4-6 Mb long and our existing 600+kb YAC contig, the existing other nucleation sites, library resources (YAC and cosmid), and mapping panels (meiotic and hybrid) are sufficient for most of that to be cloned into ordered and integrated contigs without undue difficulty. Identifying the MEN2A locus itself is more problematic, but the combination of approaches available, including a new PCR-based method to enrich for all cDNAs in a large genomic fragment, has a high probability of yielding the locus.